| Abbreviation | Designation | |
|---|---|---|
| au | außergewöhnlich (German) | |
| Au | Großraumwagen (1. Klasse, TGV) (German) Open coach (1st class) | classification |
| AU | Australia, Commonwealth of Australia | country code |
| AUS | Au (Sieg) (German) | fare point / vehicle registration plate |
| AU | Aue (Sachs) (German) | fare point / vehicle registration plate |
| 12 / KAU | Au (Sieg) (German) | station code |
| Au | ED Augsburg (1907–1920), Eisenbahndirektion Augsburg (German) | railway administration |
| Au | Rbd Augsburg / RBD Augsburg (1922–1937–1949), Reichsbahndirektion Augsburg (German) | railway administration |